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9/18/2012 Defining the Atom Atomic Structure – smallest particle of an ___________ that retains the chemical __________ of that element Atom 1 Defining the Atom 2 Dalton’s Atomic Theory (experiment based!) The Greek philosopher Democritus (460 B.C. – 370 B.C.) was among the ______ to suggest the existence of ________ (from the Greek word “atomos”) He believed that atoms were indivisible and indestructible His ideas did agree with later scientific theory, but did not explain chemical behavior, and was not based on the scientific method – but just _____________ 3 John Dalton (1766 – 1844) 1) All elements are composed of tiny indivisible particles called __________ 2) Atoms of the same element are __________. Atoms of any one element are ___________ from those of any other element. 1) Atoms of different elements combine in simple whole-number ratios to form chemical _____________ 2) In chemical reactions, atoms are combined, separated, or rearranged – but __________ 4 changed into atoms of another element. Sizing up the Atom Elements are able to be subdivided into smaller and smaller particles – these are the ___________, and they still have ___________ of that element If you could line up 100,000,000 copper atoms in a single file, they would be approximately 1 cm long Despite their small size, individual atoms are observable with instruments such as scanning tunneling (electron) 5 microscopes Structure of the Atom One change to Dalton’s atomic theory is that atoms are ___________ into subatomic particles: ____________, _________, and ____________ are examples of these fundamental particles There are many other types of particles, but we will study these three 6 1 9/18/2012 Thomson’s Atomic Model Although Thompson had the positive and negative particles in the wrong place, he is credited with discovering ___________. J. J. Thomson Thomson believed that the electrons were like plums embedded in a _________ charged “pudding,” thus it was called the “____ pudding” model. 7 Earnest Rutherford’s Experiments Conclusions: a) The nucleus is _______ b) The nucleus is _______ c) The nucleus is __________ charged This “fixed” Thompson’s plum pudding model. Rutherford is credited with discovering the ______________. 9 8 The Rutherford Atomic Model Based on his experimental evidence: The atom is mostly _________ space All the positive charge, and almost all the _______ is concentrated in a small area in the ________. He called this a “nucleus” The nucleus is composed of _______ and ___________ (they make the nucleus!) The ____________ distributed around the nucleus, and occupy most of the _________ His model was called a “nuclear model” 10 Bohr Model Modern (Wave) Model of the Atom Neils Bohr discovered _______ _______ of electrons. He said that electrons orbited the nucleus like planets orbit the ___…he was wrong about the orbiting but right that there are particular energy levels that electrons reside in. 11 The modern model of the atom consists of __________ that electrons move around in…we will discuss later. 12 2 9/18/2012 About Atoms There are presently ___ elements, thus 118 _________ kinds of ________. These atoms _________ in many different combinations and proportions to form the tremendous number of ___________ found. Experiments determined that atoms contain three ______________ particles: protons, neutrons, and electrons. Atoms have a positively charged dense central core called a nucleus. The nucleus contains protons and neutrons. Protons – __________ charge Neutrons – _________ or zero charge Protons and neutrons have about the same mass. Electrons move in the space around the nucleus called the _______________. Electrons – _________ charge Electron’s mass is _____ _____ ____ than that of neutrons and protons. 13 The nucleus is much more __________ but much ___________ than the electron cloud. If you made a model of an atom to scale – use __________ as nucleus, the end of the atom would be 2 ___________ fields away from the baseball. abbreviations commonly used: p+, no, e- 14 Subatomic Particles Particle Electron (e-) Proton (p+) Charge Mass (g) and Mass (amu) Location 9.11 x 10-28 g Approx. _ amu 1.673 x 10-24 g __ amu Neutron (no) 15 Atomic Number – tells the number of _______ in an atom. It is found on the periodic table. Ex: there are __ protons in an atom of Nitrogen, there are ___ protons in an atom of Uranium The number of ________ in an atom makes the atom what it is! Ex. Potassium has 19 protons it can never have any more or any less and still be potassium. Individual atoms are electrically _________, which means they have the _____ number of ________ as __________. Ex. An atom of copper has ___ protons and ___ electrons. 17 1.675 x 10-24 g 16 __ amu Mass Number – ____ of _______ and ___________ of a particular atom. Ex. “Chlorine-37” Ex. “Aluminum-27” Atomic number: Atomic number: Mass number: Mass number: p+: p+: e-: e-: no: no: 18 3 9/18/2012 Mass Number Naming Isotopes The number written after an element name is always the ______ number for a particular isotope of that atom. Mass number is the number of protons and neutrons in the nucleus of an isotope: Mass # = p+ + n0 p+ Nuclide n0 Oxygen - 18 carbon-12 Arsenic - 75 carbon-14 Phosphorus - 31 uranium-235 19 20 Question: Why do you think the “mass” number only includes protons and neutrons? Answer: because protons and neutrons both have a mass of __ amu, but electrons have a mass of __ amu Question: Why do you think the mass number is always a whole number? Answer: because there are always ________ numbers of protons and neutrons in an atom Complete Symbols Contain the symbol of the element, the mass number and the atomic number. Mass Superscript → number Subscript → Atomic number X 21 22 Symbols e- Mass # Find each of these: – number of protons – number of neutrons – number of electrons – Atomic number – Mass Number Symbols 80 35 23 Br If an element has an atomic number of 34 and a mass number of 78, what is the: – number of protons – number of neutrons – number of electrons – complete symbol 24 4 9/18/2012 Symbols If an element has 91 protons and 140 neutrons what is the – Atomic number – Mass number – number of electrons – complete symbol 25 Symbols If an element has 78 electrons and 117 neutrons what is the – Atomic number – Mass number – number of protons – complete symbol 26 Isotopes Isotopes Dalton was wrong about all elements of the same type being _____________ Atoms of the same element can have ___________ numbers of __________. Thus, different _________ numbers. These are called isotopes – atoms with the same number of protons but different number of neutrons...thus they have different masses. 27 Atomic Mass How heavy is an atom of oxygen? It depends, because there are different ________ of oxygen atoms. We are more concerned with the average atomic mass. (this number is found on the _________ ______) This is based on the _____________ (percentage) of each variety of that element in _________. We don’t use ________ for this mass because the numbers would be too small. 29 Elements occur in _________ as ____________ of isotopes. Ex. Chlorine exists as chlorine-__ and chlorine-__. Both have __ protons but one has __ neutrons and one has __ neutrons. •There is no way of predicting which isotopes exist for each element; these have been _______________ determined. 28 Measuring Atomic Mass Instead of grams, the unit we use is the Atomic Mass Unit (_____) Each isotope has its own atomic mass, thus we determine the average from percent abundance, which is why it is a ___________ and not a _________ number. 30 5 9/18/2012 Atomic Masses Atomic mass is the average of all the naturally occurring isotopes of that element. Isotope Symbol Carbon-12 12C Carbon-13 13C Carbon-14 14C Composition of the nucleus 6 protons 6 neutrons 6 protons 7 neutrons 6 protons 8 neutrons Carbon = 12.011 % in nature 98.89% 1.11% To get the “most __________ mass number”, __________ the atomic mass off to the nearest whole number. Example: What is the most common mass number of the following? Ag, Cu, C, Cl <0.01% 31 Draw models of lithium-5, lithium-6, and lithium-7 atoms including the correct numbers of protons, neutrons, and electrons in each. 32 IONS Ion – atom that has _______ or ____ electrons Two types: _________ – a positive ion, one that has _______ electrons _________ – a negative ion, one that has _________ electrons Atoms NEVER gain or lose __________ or ____________ (except in nuclear reactions) 33 Examples 34 Examples: Mg is a magnesium atom and has ___ protons and ___ electrons so the overall charge is ____. Mg+2 is a magnesium ion and has ___ protons and ___ electrons so the overall charge is ____. Cl is a chlorine atom and has ___ protons and ___ electrons so the overall charge is ____. Cl- is a chlorine ion has ____ protons and ___ electrons so the overall charge is ____. 35 36 6 9/18/2012 Energy Levels Maximum number of electrons Who was the first to notice that the electron cloud has different regions where electrons reside? There are various ______________ in an electron cloud. Within each energy level there are _____________ and within each sublevel there are __________. Each orbital can hold up to two electrons. Electrons move very ________ within their own ______________. 37 The total number of __________ levels an atom has corresponds to the _________ number of the atom. Periods are the ______________ rows on the PT Ex. An atom of bromine has ___ energy levels because it is in period ___ The ______ energy level, called the ____________ shell, can hold ONLY up to ______ electrons. Number of Valence e- Electron dot diagrams 3-12 and the actinides and lanthanides (B’s) 13 (3A) 14 (4A) _____________ electrons are the electrons in the __________ energy level. The atoms are arranged on the periodic table so that the ones with ___________ properties all line up in a ____________ or __________. The ____________ of valence electrons plays a big role in how the atom _____________. 40 1 (1A) 2 (2A) Max num of e- Valence Electrons 39 Group Number Energy level 1 2 3 4 5 6 7 38 More about energy levels… Energy levels (n) can hold a maximum number of 2n2 electrons. Use the number of valence electrons as _______ and space them around the ________ sides of the element’s symbol then ________ up as needed Examples: 15 (5A) 16 (6A) 17 (7A) 18 (8A) Except He (2) 41 42 7 9/18/2012 Group/Family Names to Label Alkali Metals Alkaline Earth Metals Transition Metals Lanthanides Actinides Boron Family Carbon Family Nitrogen Family Oxygen Family Halogens Noble Gases 43 44 45 46 Periods Ion Charge Prediction 47 Octet rule – atoms will ________, _________ or share electrons so that they have a ______________ ________________ shell That's ____ electrons for everything except 1st shell (H and He) which only holds __ electrons Ex. Nitrogen has ___ valence electrons so it will gain ___ to make ___. N-3 Ex. Sodium has___ valence electron so it will lose that one and the _________ shell becomes the valence shell with ___ electrons. Na48+ 8 9/18/2012 Group 1 (1A) makes ____ Group 2 (2A) makes ____ Group 3-12 (B's) are __________________ Group 13 (3A) makes ____ Group 14 (4A) makes ____ Group 15 (5A) makes ____ Group 16 (6A) makes ____ Group 17 (7A) makes ____ Group 18 (8A) makes ____ (doesn't form ions!) why? 49 Electron Configurations Examples: 50 Sublevels: s, p, d and f AUFBAU principle – electrons fill orbitals starting with the _____________ energy orbital available before filling higher energy orbitals. PAULI EXCLUSION principle – each orbital can hold at most _ electrons and they must have _______ spins (clockwise and couterclockwise) HUND'S rule – electrons occupy equal-energy orbitals so that a maximum number of _______ electrons results ex. __ __ __ not __ __ __ **spread out before pairing up** 51 52 53 54 Orbitals 9 9/18/2012 55 56 Writing electron configurations Use the periodic table as a guide. 57 58 59 60 10 9/18/2012 Abbreviated Electron Configurations More Electron Configurations Use the previous _______________ to shorten the electron configuration. 61 62 Orbital Notation Exceptions to Orbital Fill Order Use ________ to represent electrons. Any electron configuration that ends in ____ is too ___________ and actually takes an electron from the previous ___ sublevel and becomes ____. Example: 63 Another Exception 64 Examples: Any electron configuration that ends in ____ is too ___________ and actually takes an electron from the previous __ sublevel and becomes _____. Example: 65 66 11 9/18/2012 Absorption and Emission Normally, electrons in an atom are in the ____________ state, which means they are in the _______________ possible energy levels. However, these electrons can be ___________ to higher energy levels if energy is added...called _________________. If energy is absorbed and the electrons jump to higher energy levels they are now in the ________________ state. 67 Once in the excited state the atoms are ______________ and thus _______ energy when they fall back down to their original energy levels. This process is called _______________. This __________ of absorption and emission happens very fast over and over again. Atoms can be excited using _________, light, or electricity. Emission is usually in the form of __________. Different energies of light have different ___________. The light spectrum: (lower energy)ROYGBIV (higher energy) This is actually how we see colors! 68 69 12